People often misplace or otherwise lose their personal belongings such as keys, backpacks, or laptop computers. One way to find a misplaced or lost item is to attach an electronic tag, or simply referred to as a tag, to the item beforehand. The electronic tag can be a device that emits a low-energy wireless signal. A user of a computing device can use the computing device to track where the tag and the item attached to the tag are located. For example, the computing device can detect the tag when the tag is within several meters to the computing device and then alert the user of the presence of the item. If the computing device is located farther away from the tag, the computing device can request a lost-and-found service to provide a last known location of the tag. The lost-and-found server can use crowd-sourced data to determine the last known location, thereby helping the user to find the tagged item. Crowd sourcing can include monitoring signals from the tag by many mobile devices. Monitoring signals from the tag by many mobile device can consume power of the mobile devices without providing an obvious benefit to most owners of the mobile devices. For this reason, people may not wish to participate in the monitoring of the tag. Low participation in crowd sourcing can result in inaccurate or outdated information on where the tag and the item are located.